Protein Recommendations

Frame shift Variant


Frame shift
a sequence change between the translation initiation (start) and termination (stop) codon where, compared to a reference sequence, translation shifts to another reading frame.


Format: “prefix”“amino_acid”position”new_amino_acid”“fs”“Ter”“position_termination_site”, e.g. p.Arg123LysfsTer34

“prefix” = reference sequence used = p.
“amino_acid” = first amino acid changed = Arg
“position” = position = 123
“new_amino_acid” = new amino acid = Lys
“fs” = type of change is a frame shift = fs
“Ter” = termination codon = Ter / *
“position_termination_site” = position new termination site = 34


  • prefix reference sequence accepted is “p.” (protein).
  • predicted consequences, i.e. without experimental evidence (no RNA or protein analysed), should be given in parentheses, e.g. p.(Arg123LysfsTer34).
  • frame shifts can also be described using a short format; p.Arg123fs i.e. indicating the first amino acid changed, its position and “fs” without further detail.
  • frame shifts are a special type of amino acid deletion/insertion, but the description does not include the deletion from the site of the change to the C-terminal end of the protein (stop codon), like “Arg123_Leu833del”, nor the amino acid sequence inserted.
  • the position of the translation termination (stop) codon in the new reading frame is calculated starting at the first amino acid changed by the frame shift (codon 1), and ending at the first stop codon encountered (Ter# or *#)
    NOTE: the number of amino acids in the new C-terminal sequence is “#-1” amino acids
  • the description of a frame shift variant can not contain “fsTer1”, such a variant is a nonsense variant (see Substitution). The shortest frame shift variant possible contains “fsTer2”
  • for all descriptions the most C-terminal position possible of the reference sequence is arbitrarily assigned to have been changed (3’rule)
  • variants should be described on the protein level and not incorporate any knowledge regarding the change at DNA-level (see Discussion).
    • the description of a frame shift starts with the first new amino acid, this might not be first codon affected by the variant at the DNA level


  • p.Arg97ProfsTer23 (short p.Arg97fs)
    a variant with Arg97 as the first amino acid changed, shifting the reading frame, replacing it for a Pro and terminating at position Ter23.
  • p.(Tyr4*)
    the predicted consequence at the protein level of the variant ATGGATGCATACGTCACG.. to ATGGATGCATA\_GTCACG (c.12delC) is a Tyr to translation termination codon. NOTE: the variant is described as a substitution, not as a frame shift (p.Tyr4TerfsTer1)
  • p.Glu5ValfsTer5 (short p.Glu5fs)
    the predicted consequence at the protein level of the variant ATGGATGCATACGAGATGAGG to ATGGATGCATACGTGCATACGAGATGAGG.. (c.6_13dup).
  • p.Ile327Argfs*? (short p.Ile327fs)
    the predicted consequence of a frame shifting variant changes Ile327 to an Arg but the new reading frame does not encounter a new translation termination (stop) codon
  • p.Gln151Thrfs*9 (not p.His150Hisfs*10)
    the first codon at the DNA level affected by a variant is His150 and the shifted frame starts with a HisThrSer…. Since frame shift variants start with the first amino acid changed the description p.His150Hisfs*10 (or p.His150HisfsTer10) is not correct.


What do you mean with "variants should be described on the protein level and not incorporate knowledge regarding the change at the DNA-level"?

It means that protein variant descriptions should be derived from comparing the variant protein sequence with the reference protein sequence. Knowledge on the underlying change at the DNA level should not be used. E.g. when MetTrpSerSerSerHisAsp.. changes to MetTrpSerSer_HisAsp.. this is described as p.Ser5del. The information that at the DNA level the change is ..ATGTGGTCCAGTTCCCACGAT.. to ..ATGTGGTCC_TCCCACGAT.., so the codon for Ser4 is deleted, is not used; the description p.Ser4del is not correct.